Image pickup apparatus

ABSTRACT

An image pickup apparatus having a continuous shooting mode in which images are captured for recording in response to an image capture instruction, wherein respective development process for each image is performed before capturing a subsequent image for recording in the continuous shooting mode, includes a focus control unit and a control unit. The focus control unit detects a focal point of a focus lens. The control unit controls movement of the focus lens and controls the capturing of an image. After the control unit controls the movement of the focus lens using the focus control unit and captures an image for recording in the continuous shooting mode, the control unit moves the focus lens to a predetermined position and then moves the focus lens across a predetermined range from the predetermined position to perform the scanning using the focus control unit during the development process of the captured image.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 11/672,366, filed on Feb. 7, 2007, which claims priority fromJapanese Patent Application No. 2006-042449, filed Feb. 20, 2006, all ofwhich are hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image pickup apparatus capable ofperforming focus control during a continuous shooting interval.

2. Description of the Related Art

A focus control apparatus used in electronic cameras is known thatperforms focus control by a contrast detection auto focus method. In thecontrast detection auto focus method, the focus control apparatusdetermines the lens position that maximizes the high-frequency componentof a luminance signal of a subject image formed on an image pickupdevice to be a focused focal point. Hereinafter, the high-frequencycomponent is referred to as a “focus evaluation value”.

In addition, a focus control apparatus is known that performs focuscontrol on the basis of a passive and active auto focus (AF). In thepassive and active AF, the focus control apparatus receives a light beamreflected off a subject using a lens other than the imaging-capturinglens and a dedicated sensor. In addition, some focus control apparatusesemploy the two above-described techniques and selects one of the twotechniques as needed.

In recent years, many electronic cameras have employed the contrastdetection auto focus method for a focus control apparatus. However,unlike a method of using a dedicated AF sensor, this method requires ascan operation of a focus lens in a light axis direction thereof, andtherefore, additional time is generally required before focusing isachieved. Accordingly, in a mode that needs to reduce the shooting lag(such as in a continuous shooting mode), focus control is performed onlyonce before starting the continuous shooting. In the subsequentcontinuous shooting operation, focus control is not performed. As such,Japanese Patent Laid-Open No. 2001-255456 describes a technique ofreducing the increase in the time lag by switching between a focuscontrol apparatus based on the contrast detection method and a focuscontrol apparatus based on the passive/active AF using a dedicatedsensor.

However, if an electronic camera includes a dedicated sensor forrealizing the passive or active AF in addition to the focus controlapparatus based on the contrast detection method, the body size and thefabrication cost of the electronic camera are increased. Therefore, itis difficult to apply this technology to all the electronic cameras.

The known technology for using a focus control apparatus based on thecontrast detection method has the following disadvantages. For example,if the focus is locked at the focus lens position for the first imagecapturing operation in a continuous shooting mode and a subject movesbeyond the depth of field during a continuous shooting operation, allthe subsequent captured images are out of focus. In contrast, if thefocus is adjusted by the contrast detection method every time an imageis captured during a continuous shooting operation, the time intervalbetween the image capturing operations is increased.

SUMMARY OF THE INVENTION

The present invention provides an image pickup technology forsignificantly reducing a continuous shooting interval time and realizingfocus control by the contrast detection method during the continuousshooting interval time.

According to an embodiment of the present invention, an image pickupapparatus is provided having a continuous shooting mode in which aplurality of images are captured for recording in response to an imagecapture instruction. The image pickup apparatus includes a focus controlunit configured to detect a focal point of a focus lens by scanning thefocus lens in a light axis direction thereof and controlling movement ofthe focus lens so that the focus lens is focused at the focal point; anda control unit configured to control movement of the focus lens and tocontrol the capturing of an image. After the control unit controls themovement of the focus lens using the focus control unit and captures animage for recording in the continuous shooting mode, the control unitcontrols the movement of the focus lens using the focus control unitbefore capturing the subsequent image for recording concurrently withperformance of a development process of the captured image.

According to another aspect of the present invention, the control of themovement of the focus lens for the subsequent image capturing operationfor recording by the focus control unit is performed concurrently with areadout process of an exposure image from an image pickup device.

According to yet another aspect of the present invention, the control ofthe movement of the focus lens for the subsequent image capturingoperation for recording by the focus control unit includes controllingthe movement of the focus lens to a scan start position for detectingthe focused focal point.

Moreover, according to another aspect of the present invention, in thecontinuous shooting mode, a position from which detection of the focalpoint is performed by the focus control unit is determined on the basisof the position of the focal point detected during capturing of theprevious image.

Additionally, according to another aspect of the present invention, animage pickup apparatus is provided having a continuous shooting mode inwhich a plurality of images are captured for recording in response to animage capture instruction. The image pickup apparatus includes a focuscontrol unit configured to detect a focal point of a focus lens byscanning the focus lens in a light axis direction thereof andcontrolling movement of the focus lens so that the focus lens is focusedat the focal point; a memory configured to temporarily store thecaptured images; an instructing unit configured to instruct a monitor tooutput the images without recording the images stored in the memory; anda control unit configured to control movement of the focus lens and tocontrol the capturing of an image. After the control unit controls themovement of the focus lens using the focus control unit and captures animage for recording in the continuous shooting mode, the control unitcontrols the movement of the focus lens using the focus control unitbefore the instruction unit instructs the monitor to output one of theimages.

According to yet another aspect of the present invention, in thecontinuous shooting mode, a position from which detection of the focalpoint is performed by the focus control unit is determined on the basisof the position of the focal point detected during capturing of theprevious image.

Furthermore, according to yet another aspect of the present invention, amethod is provided which may be utilized in an image pickup apparatushaving a continuous shooting mode in which a plurality of images arecaptured for recording in response to an image capture instruction, theimage pickup apparatus including a focus control unit configured todetect a focal point of a focus lens by scanning the focus lens in alight axis direction thereof and controlling movement of the focus lensso that the focus lens is focused at the focal point; and a control unitconfigured to control movement of the focus lens and to control thecapturing of an image. The method includes controlling the movement ofthe focus lens; capturing an image for recording in the continuousshooting mode; and controlling the movement of the focus lens beforecapturing a subsequent image for recording concurrently with performanceof a development process of the captured image.

And furthermore, according to another aspect of the present invention, acomputer readable medium is provided containing computer-executableinstructions for controlling an image pickup apparatus having acontinuous shooting mode in which a plurality of images are captured forrecording in response to an image capture instruction, the image pickupapparatus including a focus control unit configured to detect a focalpoint of a focus lens by scanning the focus lens in a light axisdirection thereof and controlling movement of the focus lens so that thefocus lens is focused at the focal point; and a control unit configuredto control movement of the focus lens and to control the capturing of animage. The computer readable medium includes computer-executableinstructions for controlling the movement of the focus lens;computer-executable instructions for capturing an image for recording inthe continuous shooting mode; and computer-executable instructions forcontrolling the movement of the focus lens before capturing a subsequentimage for recording concurrently with performance of a developmentprocess of the captured image.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example circuit of an electronic cameraaccording to first to third exemplary embodiments of the presentinvention.

FIG. 2 is a flow chart of an exemplary operation of the electroniccamera according to the first exemplary embodiment of the presentinvention.

FIG. 3 is a flow chart of an exemplary continuous AF subroutine shown inFIG. 2 according to an aspect of the present invention.

FIG. 4 is a flow chart of an exemplary AF operation subroutine shown inFIG. 2 according to an aspect of the present invention.

FIG. 5 is a diagram illustrating an exemplary method for setting a scanrange shown in FIG. 4 according to an aspect of the present invention.

FIG. 6 is a flow chart of an exemplary scan subroutine shown in FIG. 4according to an aspect of the present invention.

FIG. 7 is a flow chart of an exemplary focus determination subroutineshown in FIG. 4 according to an aspect of the present invention.

FIG. 8 is a flow chart of an exemplary subroutine for examining amonotonic decreasing of a curve of a focus evaluation value towardsinfinity according to an aspect of the present invention.

FIG. 9 is a flow chart of an exemplary subroutine for examining amonotonic decreasing of a curve of a focus evaluation value in aproximal direction according to an aspect of the present invention.

FIG. 10 is a diagram illustrating the concept of determination of afocus evaluation value according to an aspect of the present invention.

FIG. 11 is a flow chart of an exemplary image capturing processsubroutine shown in FIG. 2 according to an aspect of the presentinvention.

FIGS. 12A and 12B illustrate a flow chart of an exemplary continuousshooting interval AF process according to the first exemplary embodimentaccording to an aspect of the present invention.

FIG. 13 is a timing diagram of an exemplary continuous shooting intervalAF process according to the first exemplary embodiment.

FIG. 14 is a flow chart of an exemplary image capturing processsubroutine according to the second exemplary embodiment.

FIG. 15 is a flow chart of an exemplary continuous shooting interval AFprocess A according to the second exemplary embodiment.

FIGS. 16A and 16B illustrate a flow chart of an exemplary continuousshooting interval AF process B according to the second exemplaryembodiment.

FIG. 17 is an exemplary timing diagram of the continuous shootinginterval AF process according to the second exemplary embodiment of thepresent invention.

FIG. 18 is an exemplary timing diagram of the continuous shootinginterval AF process according to the third exemplary embodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments of the present invention are now hereindescribed below.

First Exemplary Embodiment

A first exemplary embodiment of the present invention is described belowwith reference to the accompanying drawings. In the first exemplaryembodiment, the focus control operation during a continuous shootinginterval is achieved even in a system that cannot compute the focusevaluation value and perform image processing on a main exposure imagesignal at the same time due to resource contention.

FIG. 1 is a block diagram of an exemplary circuit configuration of anelectronic camera system according to the first exemplary embodiment ofthe present invention. The electronic camera system includes animage-capturing lens 101 having a zoom mechanism, an aperture andshutter 102 for controlling the amount of light, and an AE processingunit 103, a focus lens 104 for focusing light on an image pickup device,an AF processing unit 105, a flash 106, an EF processing unit 107, andan image pickup device 108 serving as a light detecting unit or aphotoelectric conversion unit for converting light reflected off asubject to an electrical signal. The electronic camera system furtherincludes an A/D converter 109. The A/D converter 109 includes a CDScircuit for reducing output noise of the image pickup device 108 and anon-linear amplifier circuit that operates before A/D conversion isperformed. The electronic camera system further includes an imageprocessing unit 110 and a white-balance (WB) processing unit 111.

The electronic camera system further includes a format conversion unit112, a high-speed internal memory 113, such as a random access memory(hereinafter referred to as a “DRAM”), an image recording unit 114including a recording medium (e.g., a memory card) and an interfacethereof, and a system controller 115 for controlling the system (e.g.,the image capturing sequence). The electronic camera system furtherincludes an image display memory 116 (hereinafter referred to as a“VRAM”) and an operation display unit 117 for displaying operationassistance information and the camera state. In addition, the operationdisplay unit 117 displays an image to be captured and AF areas during ashooting operation. The electronic camera system further includes anoperation unit 118 for a user to externally operate the electroniccamera system.

The electronic camera system further includes a shooting mode switch 119for setting a shooting mode, such as a program mode, a landscape mode, aportrait mode, and a sport mode, and a drive mode switch (SW) 120 forsetting a drive mode, such as a single shooting mode, a continuousshooting mode, and a self-timer shooting mode. The electronic camerasystem further includes an AF mode switch 121 for switching between acontinuous AF mode in which a subject is focused on at all times and asingle AF mode in which a subject is focused on in one scanningoperation immediately before the shooting operation, and a main switch122 for powering on the electronic camera system. The electronic camerasystem further includes a standby switch 123 (hereinafter, this switchis also referred to as a “switch SW1”) for starting a shooting standbyoperation, such as the AF and AE operations, and a shooting switch 124(hereinafter, this switch is also referred to as a “switch SW2”) forstarting an actual shooting operation after the switch SW1 is operated.The electronic camera system further includes a monitor control unit 125for controlling the output of an image to a monitor under the control ofthe system controller 115.

The DRAM 113 is used for a high-speed buffer serving as an image storingunit that temporarily stores an image or a working memory used forcompression or decompression of an image. The operation unit 118includes, for example, a menu button for inputting a variety ofsettings, such as settings for the shooting function and the imageplayback function of the image pickup apparatus, a zoom lever forzooming the imaging-capturing lens, and an operation mode selectorswitch for switching between a shooting mode and a playback mode.

FIG. 2 is a flow chart illustrating the operation of the electroniccamera according to the first exemplary embodiment of the presentinvention starting from the power-on. This operation is performed by thesystem controller 115.

At step S201, the system controller 115 determines whether the AF modeis a continuous AF mode or a single AF mode. If the AF mode is acontinuous AF mode (YES in step S201), the process proceeds to stepS202. Otherwise (NO in step S201), the process proceeds to step S203. Atstep S202, a continuous AF process is performed in accordance with aflow chart of FIG. 3, which is described later. At step S203, the on/offstate of the switch SW1 is checked. If the switch SW1 is ON (YES in stepS203), the process proceeds to step S204. Otherwise (NO in step S203),the process returns to step S201. That is, operation of the switch SW1starts an image capturing standby operation for the AF and AE processes.

At step S204, the system controller 115 determines whether the AF modeis a continuous AF mode or a single AF mode. If the AF mode is acontinuous AF mode (YES in step S204), the process proceeds to stepS205, where the currently running continuous AF operation is stopped.The process then proceeds to step S206. At step S206, the AE processingunit 103 performs an AE operation for the AF operation using the outputfrom the image processing unit 110. At step S207, AF operation isperformed in accordance with a flow chart of FIG. 4, which is describedbelow. At step S208, the on/off state of the switch SW1 is checked. Ifthe switch SW1 is ON (YES in step S208), the process proceeds to stepS209. Otherwise (NO in step S208), the process returns to step S201.

At step S209, the on/off state of the switch SW2 is checked. If theswitch SW2 is ON (YES in step S209), the process proceeds to step S210.Otherwise (NO in step S209), the process returns to step S208, where thefocus is locked until the switch SW1 is turned OFF or the switch SW2 isturned ON. That is, the switch SW2 starts an image capturing operationafter the switch SW1 is operated. At step S210, the AE processing forthe subsequent main exposure is performed. At step S211, the imagecapturing process is performed in accordance with a flow chart of FIG.11, which is described below. This image capturing process includes acontinuous shooting operation, a focus control operation during thecontinuous shooting interval, and a determination process fordetermining whether the continuous shooting operation has started. Afterstep S211 is completed, the process returns to step S201.

An exemplary subroutine of the continuous AF process at step S202 ofFIG. 2 is described next with reference to a flow chart of FIG. 3.

At step S301, the system controller 115 acquires a focus evaluationvalue that indicates the contrast ratio of the captured image. At stepS302, it is determined whether a peak detection flag is TRUE. If thepeak detection flag is TRUE (YES in step S302), the process proceeds tostep S317. Otherwise (NO in step S302), the process proceeds to stepS303. At step S303, the system controller 115 acquires the currentposition of the focus lens 104. At step S304, an acquirement counterused for counting the acquirement of the focus evaluation value and theacquirement of the current position of the focus lens 104 is incrementedby one. This acquirement counter is initialized to zero in aninitialization process (not shown) in advance. At step S305, it isdetermined whether the value of the acquirement counter is one. If thevalue of the acquirement counter is one (YES in step S305), the processproceeds to step S307. Otherwise (NO in step S305), the process proceedsto step S306.

At step S306, it is determined whether the current focus evaluationvalue is greater than the previous focus evaluation value. If thecurrent focus evaluation value is greater than the previous focusevaluation value (YES in step S306), the process proceeds to step S307.Otherwise (NO in step S306), the process proceeds to step S313. At stepS307, the current focus evaluation value is considered to be a maximumfocus evaluation value and is stored in an internal calculation memory(not shown) of the system controller 115. Thereafter, at step S308, thecurrent position of the focus lens 104 is considered to be a peak pointof the focus evaluation value and is stored in the internal calculationmemory of the system controller 115. At step S309, the current focusevaluation value is set to be the previous focus evaluation value and isstored in the internal calculation memory of the system controller 115.

At step S310, it is determined whether the current position of the focuslens 104 corresponds to an end of a scan range for detecting thefocusing state by acquiring the focus evaluation value. If the currentposition of the focus lens 104 corresponds to an end of the scan range(YES in step S310), the process proceeds to step S311. Otherwise (NO instep S310), the process proceeds to step S312. At step S311, the movingdirection of the focus lens 104 is reversed. Thereafter, at step S312,the focus lens 104 is moved by a predetermined distance.

However, if it is determined at step S306 that the current focusevaluation value is not greater than the previous focus evaluation value(NO in step S306) and the process proceeds to step S313, it isdetermined whether (the maximum focus evaluation value—the current focusevaluation value) is greater than a predetermined value. If (the maximumfocus evaluation value—the current focus evaluation value) is greaterthan a predetermined value (YES in step S313), the process proceeds tostep S314. Otherwise (NO in step S313), the process proceeds to stepS309. Here, if (the maximum focus evaluation value—the current focusevaluation value) is greater than the predetermined value, that is, ifthe current focus evaluation value is decreased from the maximum focusevaluation value by more than the predetermined value, the maximum focusevaluation value is considered to be a value when the focus is at a peakpoint. If (the maximum focus evaluation value—the current focusevaluation value) is greater than the predetermined value and theprocess proceeds to step S314, the focus lens 104 is moved to the peakpoint which is stored at step S308 and at which the focus evaluationvalue is maximized. At step S315, the peak detection flag is set toTRUE. At step S316, the acquirement counter is set to zero.

If it is determined at step S302 that the peak detection flag is TRUE(YES in step S302) and the process proceeds to step S317, it isdetermined whether the focus evaluation value fluctuates with respect tothe maximum focus evaluation value by more than a predetermined ratio.If the focus evaluation value fluctuates with respect to the maximumfocus evaluation value by more than the predetermined ratio (YES in step317), the process proceeds to step S319. In contrast, if the fluctuationis small (NO in step S317), the process proceeds to step S318. At stepS318, the position of the focus lens 104 remains unchanged. In contrast,at step S319, the peak detection flag is set to FALSE in order toredetermine the position of the focus lens that maximizes the focusevaluation value. The maximum focus evaluation value and the peak pointare reset.

In this way, the focus lens 104 is driven so that the focus is always onthe subject in the continuous AF process.

An exemplary subroutine of the AF operation at step S207 shown in FIG. 2is described next with reference to a flow chart of FIG. 4.

At step S401, the system controller 115 determines whether the AF modeis a continuous AF mode or a single AF mode. If the AF mode is acontinuous AF mode (YES in step S401), the process proceeds to stepS402. Otherwise (NO in step S401), the process proceeds to step S404. Atstep S402, it is determined whether the peak detection flag shown in theflow chart of FIG. 3 is TRUE. If the peak detection flag is TRUE (YES instep S402), the process proceeds to step S403. However, if the peakdetection flag is FALSE (NO in step S402), the process proceeds to stepS404.

At step S403, since the focus lens 104 is located near the in-focusposition at which the focus evaluation value is maximized due to thecontinuous AF operation, the system controller 115 determines a scanrange having a predetermined narrow scan width at the center of which isthe current focus lens position in order to improve the accuracy of thefocusing operation. Here, the scan range is determined so that thenumber of scan data samples required for the determination of thein-focus state shown in FIG. 7 is obtained and the scan time is not toolong. At step S404, the entire AF available area in the current set modeis determined to be the scan range.

At step S405, the scan operation is performed over the scan rangedetermined at step S403 or step S404 in accordance with a flow chart ofFIG. 6, which is described below. At step S406, the in-focus state isdetermined using scan data stored at step S405 in accordance with a flowchart of FIG. 7, which is described below. At step S407, if the resultof the determination of the in-focus state is “OK” (YES in step S407),the process proceeds to step S410. However, if the result of thedetermination of the in-focus state is “Not OK” (NO in step S407), theprocess proceeds to step S408. At step S408, it is determined whetherthe scan has been completed over the entire AF available area in thecurrent set mode. If the scan has been completed over the entire AFavailable area (YES in step S408), the process proceeds to step S409.Otherwise (NO in step S408), the process returns to step S404. At stepS409, the focus lens 104 is moved to a predetermined position referredto as a “fixed point” and then the process returns. In contrast, at stepS410, the focus lens 104 is moved to a peak point calculated at stepS406 and then the process returns.

The AF operation described above is applied to the continuous shootingmode and the single shooting mode.

A scan subroutine performed at step S405 of FIG. 4 is described nextwith reference to a flow chart of FIG. 6.

At step S601, the focus lens 104 is moved to a scan start position. Thescan start position is determined to be at one end of the determinedscan range. At step S602, the focus evaluation value of the AF area setin the image capturing screen and the position of the focus lens 104 arestored in the internal calculation memory of the system controller 115.At step S603, it is determined whether the lens position corresponds tothe scan end position. If the lens position corresponds to the scan endposition (YES in step S603), the process proceeds to step S605.Otherwise (No in step S603), the process proceeds to step S604. The scanend position is determined to be the other end of the determined scanrange. At step S604, the focus lens 104 is driven to move in apredetermined direction by a predetermined distance, and then theprocess returns to step S602. At step S605, the peak point of the focusevaluation value is calculated on the basis of the focus evaluationvalue stored at step S602 and the lens position thereof, and then theprocess returns.

An exemplary focus determination subroutine performed at step S406 ofFIG. 4 is described next with reference to FIGS. 7 to 10.

Except for a special condition, such as when foreground and backgroundsubjects exist in the frame, the focus evaluation value exhibits, asshown in FIG. 10, a mountain-shaped curve in a graph where the abscissarepresents the position of a focus lens and the ordinate represents thefocus evaluation value. Accordingly, the in-focus state is determined bydetermining whether the curve of the focus evaluation value ismountain-shaped. The mountain shape is determined on the basis of adifference between the maximum focus evaluation value and the minimumfocus evaluation value, the length of a tilted portion at an angle ofmore than or equal to a predetermined value (SlopeThr), and thegradients of the tilted portions. The determination result is output inthe form of one of the following two values:

“OK”: Focus control is possible using the peak point of the focusevaluation value; and

“Not OK”: The contrast of a subject is insufficient or the subject islocated out of the scanned distance range.

Here, as shown in FIG. 10, the end points of the slopes starting fromthe top of the mountain-shaped curve (i.e., a point A) are referred toas points D and E. Let L denote the width of the mountain-shaped curve(i.e., the distance between the points D and E) and SL denote a sum(SL1+SL2), where SL1 is a difference in focus evaluation value betweenthe points A and D and SL2 is the difference in focus evaluation valuebetween the points A and E.

FIG. 7 is a detailed flow chart of the focus determination subroutineperformed at step S406 of FIG. 4.

At step S701, a maximum focus evaluation value max, a minimum focusevaluation value min, and a scan point io that provides the maximumfocus evaluation value max are computed. At step S702, a variable L thatindicates the width of the mountain-shaped curve of the focus evaluationvalue and a variable SL that indicates the gradient of themountain-shaped curve are initialized to zero. At step S703, it isdetermined whether the scan point io that provides the maximumevaluation value is located at a distal end of a predetermined scanrange. If the scan point io is not located at the distal end of thepredetermined scan range (NO in step S703), the process proceeds to stepS704, where monotonic decreasing of the curve of the focus evaluationvalue towards infinity is examined. However, if the scan point io islocated at the distal end of the predetermined scan range (YES in stepS703), the process at step S704 is skipped and the process proceeds tostep S705.

The process of examining monotonic decreasing of the curve of the focusevaluation value towards infinity at step S704 is described next withreference to FIG. 8. FIG. 8 is a flow chart of this process.

At step S801, a counter variable i is initialized to io. At step S802,the difference between a focus evaluation value d[i] at a scan point iand a focus evaluation value d[i−1] at a scan point i−1 which is closerto infinity than the scan point i by one scan point is compared with aconstant value SlopeThr. If d[i]−d[i−1]≧SlopeThr, it is determined thatmonotonic decreasing of the curve of the focus evaluation value towardsinfinity occurs (YES at step S802). The process then proceeds to stepS803. At step S803, the variable L that represents the length of aportion (the width of the mountain-shaped curve) where the curve of thefocus evaluation value is sloped at an angle greater than or equal to apredetermined value and the variable SL that represents the decrease inthe monotonic decreasing interval are updated as follows:

L=L+1

SL=SL+(d[i]−d[i−1])

However, if d[i]−d[i−1]<SlopeThr, it is determined that monotonicdecreasing of the curve of the focus evaluation value towards infinitydoes not occur (NO in step S802). The process of examining monotonicdecreasing of the curve of the focus evaluation value towards infinityis completed. The process then proceeds to step S705.

When the system controller 115 continues the process of examiningmonotonic decreasing of the curve of the focus evaluation value towardsinfinity, the process proceeds to step S804. At step S804, the detectionpoint is moved towards infinity by one scan point by setting i=i+1. Atstep S805, it is determined whether the counter i is equal to the valueof the distal end of the predetermined scan range (i.e., a value zero).If the counter i is equal to zero, that is, if the start point of thescan for detecting the monotone decreasing reaches the distal end of thepredetermined scan range (YES in step S805), the process of examiningmonotonic decreasing of the curve of the focus evaluation value towardsinfinity is completed. Thereafter, the process proceeds to step S705shown in FIG. 7. In this way, the process of examining monotonicdecreasing of the curve of the focus evaluation value towards infinityis performed starting from i=io.

Referring back to FIG. 7, at step S705, it is determined whether thescan point io that provides the maximum value is at the proximal end ofthe predetermined scan range. If the scan point io is not at theproximal end of the predetermined scan range (NO in step S705), theprocess proceeds to step S706. At step S706, the monotonic decreasing ofthe curve of the focus evaluation value in the proximal direction isexamined. However, if the scan point is at the proximal end of thepredetermined scan range (YES in step S705), the process at step S706 isskipped and the process proceeds to step S707.

An exemplary process of examining the monotonic decreasing of the curveof the focus evaluation value in the proximal direction at step S706 isdescribed next with reference to FIG. 9. FIG. 9 is a flow chart of thisprocess.

At step S901, a counter variable i is initialized to io. At step S902,the difference between a focus evaluation value d[i] at a scan point iand a focus evaluation value d[i+1] at a scan point i+1 which is closerto the proximal end point than the scan point i by one scan point iscompared with the constant value SlopeThr. If d[i]−d[i+1]≧SlopeThr, itis determined that the monotonic decreasing of the curve of the focusevaluation value in the proximal direction occurs (YES in step S902).The process then proceeds to step S903. At step S903, the variable Lthat represents the length of a portion (the width of themountain-shaped curve) where the curve of the focus evaluation value issloped at an angle greater than or equal to a predetermined value andthe variable SL that represents the decrease in the monotonic decreasinginterval are updated as follows:

L=L+1

SL=SL+(d[i]-d[i+1])

However, if d[i]−d[i+1]<SlopeThr, it is determined that the monotonicdecreasing of the curve of the focus evaluation value in the proximaldirection does not occur (NO in step S902). The process of examining themonotonic decreasing of the curve of the focus evaluation value in theproximal direction is completed. The process then proceeds to step S707.

When the system controller 115 continues the process of examining themonotonic decreasing of the curve of the focus evaluation value in theproximal direction, the process proceeds to step S904. At step S904, thedetection point is moved in the proximal direction by one scan point bysetting i=i+1. At step S905, it is determined whether the counter i isequal to the value of the proximal end of the predetermined scan range(i.e., a value N). If the counter i is equal to N, that is, if the startpoint of the scan for detecting the monotone decreasing reaches theproximal end of the predetermined scan range (YES in step S905), theprocess for examining the monotonic decreasing of the curve of the focusevaluation value in the proximal direction is completed. Thereafter, theprocess proceeds to step S707 shown in FIG. 7. In this way, the processof examining the monotonic decreasing of the curve of the focusevaluation value in the proximal direction is performed starting fromi=io.

After the processes for examining monotonic decreasing of the curve ofthe focus evaluation value towards infinity and in the proximaldirection are completed, a variety of coefficients are compared withthreshold values thereof to determine whether the obtained curve of thefocus evaluation value has a mountain shape. Thus, the determination asto “OK” or “Not OK” is made.

Referring back to FIG. 7 again, at step S707, if the scan point io thatprovides the maximum focus evaluation value is at the proximal end ofthe predetermined scan range and the difference between a focusevaluation value d[n] at the proximal scan point n and a focusevaluation value d[n−1] at a scan point n−1 which is closer to infinitythan the scan point n by one scan point is greater than or equal to theconstant value SlopeThr (YES in step S707), the process proceeds toS711. Otherwise (NO in step S707), the process proceeds to S708. At stepS708, if the scan point io that provides the maximum focus evaluationvalue is at the distal end of the predetermined scan range and thedifference between a focus evaluation value d[0] at the distal scanpoint 0 and a focus evaluation value d[1] at a scan point 1 which iscloser in the proximal direction than the scan point 0 by one scan pointis greater than or equal to the constant value SlopeThr (YES in stepS708), the process proceeds to S711. Otherwise (NO in step S708), theprocess proceeds to S709.

At step S709, if the three following conditions are satisfied: (a) thevariable L that represents the length of a portion (the width of themountain-shaped curve) where the curve of the focus evaluation value issloped at an angle greater than or equal to a predetermined value isgreater than or equal to a predetermined value Lo; (b) the averagegradient SL/L of the sloped portion is greater than or equal to apredetermined value SLo/Lo; and (c) the difference between a maximumfocus evaluation value max and a minimum focus evaluation value min isgreater than or equal to a predetermined value (YES in step S709), theprocess proceeds to step S710. Otherwise (NO in step S709), the processproceeds to step S711. At step S710, since the obtained curve of thefocus evaluation value has a mountain shape and the focus control of thesubject is available, the determination result is “OK”. At step S711,since the obtained curve of the focus evaluation value does not have amountain shape and the focus control of the subject is not available,the determination result is “Not OK”. In this way, the focusdetermination at step S406 in the flow chart of FIG. 4 is made.

An exemplary subroutine of the image capturing process at step S211 ofFIG. 2 is described next with reference to a flow chart of FIG. 11.According to the first exemplary embodiment, the image capturingsubroutine includes the determination of execution of a continuousshooting operation and focus control during a continuous shootinginterval.

At step S1100 shown in FIG. 11, the monitor control unit 125 stopsdisplaying a live image. At step S1101, the image pickup device 108 isexposed. An image formed on the surface of the image pickup device 108is photoelectrically converted to an analog signal. At step S1102, theanalog signal is transferred to the A/D converter 109. The A/D converter109 performs pre-processing including reduction of output noise of theimage pickup device 108 and a non-linear process first. The A/Dconverter 109 then converts the analog signal to a digital signal. Atstep S1103, it is determined whether the current set mode is acontinuous shooting mode. If the current set mode is a continuousshooting mode (YES in step S1103), the process proceeds to step S1104.Otherwise (NO in step S1103), the process proceeds to step S1106.

At step S1104, it is determined whether the switch SW2 is continuouslydepressed. If the ON state of the switch SW2 is maintained (YES in stepS1104), the process proceeds to a continuous shooting interval AFprocessing subroutine at step S1105. The continuous shooting interval AFprocessing at step S1105 is described below with reference to FIGS. 12and 13.

At step S1106, a signal output from the A/D converter 109 is subjectedto white balance adjustment by the white-balance (WB) processing unit111. The image processing unit 110 corrects this signal into anappropriate output image signal. At step S1107, the format conversionunit 112 converts the format of the output image signal to, for example,a JPEG format. The converted output image signal is temporarily storedor recorded in the DRAM 113 serving as a working memory. As used herein,the series of processes from steps S1106 to S1107 is referred to as a“development process”.

At step S1108, a write request is registered. The write request is usedfor requesting performance of a data write process (delayed writeprocess) in which data is written to a recording medium concurrentlywith another process. That is, the write request is used to instruct theimage recording unit 114 to store data in the DRAM 113 serving as aworking memory in a memory of the camera or on an external recordingmedium (such as a memory card) loaded in the camera. Thus, the liveimage can be displayed during storing of data on the recording medium.

At step S1109, the display of the live image that has been stopped atstep S1100 is resumed. As used herein, the term “live image” refers to acaptured image for which image data is not to be record on the recordingmedium. The monitor control unit 125 controls the monitor to displaythis live image. By viewing the live image, a photographer can monitorthe angle of field and the subject even during the continuous shootingoperation.

As noted above, if the continuous shooting mode is set and the switchSW2 is depressed, the continuous shooting operation is continuouslyexecuted. If one of the above-described conditions is not satisfied, asingle shooting operation is executed.

The exemplary continuous shooting interval AF processing subroutine atstep S1105 shown in FIG. 11 is described next with reference to FIGS. 5,12, and 13. FIG. 5 illustrates the setting of the scan range. FIG. 12 isa flow chart of an exemplary continuous shooting interval AF processing.FIG. 13 is an exemplary timing diagram when the continuous shootinginterval AF processing shown by the flow chart in FIG. 12 is executedconcurrently with other processes.

The development process is started at step S1201 shown in FIG. 12A. Thedevelopment process is started immediately after the readout operationof the main exposure image signal shown in FIG. 13 has been completed.At step S1202, it is determined whether this image capturing operationis a second image capturing operation of the continuous shootingoperation. If this image capturing operation is a second image capturingoperation of the continuous shooting operation (YES in step S1202), theprocess proceeds to step S1206. Otherwise (NO in step S1202), theprocess proceeds to step S1203.

At step S1206, the current position, that is, the position (FP1) of thefocus lens in the first image capturing operation is determined to be atthe central point of the scan range (see a position (2) in FIG. 5). Thesame widths of the scan range are determined so that the continuousshooting interval time is not increased, for example, the AF operationis completed within the continuous shooting interval time. Note that, inthe first image capturing operation of the continuous shooting, theentire range that enables the AF in the set mode is determined to be thescan range. Additionally, the electronic camera is in an in-focus statedue to the continuous AF operation. The position of the focus lens 104is located at a peak point.

At step S1203, it is determined whether this image capturing operationis a third image capturing operation of the continuous shooting. If thisimage capturing operation is a third image capturing operation (YES instep S1203), the process proceeds to step S1205. Otherwise (NO in stepS1203), the process proceeds to step S1204. At step S1205, the twoin-focus position information items for the first image capturingoperation and the second image capturing operation of the continuousshooting operation are available as in-focus position historyinformation. Accordingly, as shown by a position (3) in FIG. 5, assumingthat the continuous shooting interval time is constant, the scan middleposition ObjP3 can be obtained by subject estimation using a first-orderapproximation as follows:

ObjP3=FP2+(FP2−FP1)×FpAdj3  (1)

where

FP1: the position of the focus lens at the first shot

FP2: the position of the focus lens at the second shot

FpAdj3: a parameter in the range between 0 (previous position) and 1(estimation).

Note that the parameter FpAdj(n) is a parameter for weighting theestimation result of the subject and the immediately previous in-focusposition. The value of the parameter FpAdj(n) ranges from 0 to 1. At theposition of the focus lens in FIG. 5, FpAdj(n)=1. As in step S1206, thewidths of the scan range are set to be the same.

At step S1204, at least three previous in-focus position informationitems are available as in-focus position history information.Accordingly, as shown by a position (4) in FIG. 5, assuming that thecontinuous shooting interval time is constant, the scan middle positionObjP4 can be obtained by subject estimation using a second-orderapproximation as follows:

ObjP4=(FP1−3·FP2+3·FP3)×FpAdj4+FP3×(1−FpAdj4)=(FP1−3·FP2+2·FP3)×FpAdj4+FP3  (2)

where

FP3: the position of the focus lens in the third image capturingoperation.

Similarly, the scan middle position ObjP(n) in the nth image capturingoperation can be obtained using a second-order approximation as follows:

ObjP(n)={FP1(n−3)−3·FP(n−2)+2·FP(n−1)}×FpAdj(n)+FP(n−1)  (3)

Here, as in step S1206, the widths of the scan range are determined tobe the same. The process then proceeds to step S1207. At step S1207,moving of the focus lens 104 to the scan start position in the scanrange determined at steps 1204 to 1206 is started. Accordingly, as shownin FIG. 13, the development process is concurrently performed while thefocus lens 104 is moved.

At step S1208, it is determined whether the focus lens 104 has reachedthe scan start position. If the focus lens 104 has reached the scanstart position (YES in step S1208), the process proceeds to step S1209.However, if the focus lens 104 has not reached the scan start positionyet, the process returns to step S1208, where the system controller 115waits for the completion of the movement of the focus lens 104. At stepS1209, it is determined whether the development process has beencompleted. If the development process has not been completed yet (NO instep S1209), the process returns to step S1209, where the systemcontroller 115 waits for the completion of the development process.However, if the development process has been completed (YES in stepS1209), the process proceeds to step S1210. Accordingly, the processproceeds to the next processing only when the movement of the focus lens104 and the development process have been completed.

At step S1210, the computation of the focus evaluation value is started.In addition, the display of a live image is started at step S1211. Thelive image that is started to be displayed again is that which wasstopped being displayed immediately before the main exposure wasperformed at step S1100. The term “main exposure” refers to an exposureof an image to be recorded as a still image. While this main exposure isperformed and the development process of data of the exposure image isperformed, a live image cannot be generated. Therefore, the display ofthe current live image is stopped. At that time, as shown in FIG. 13,the drive of the image pickup device 108 (the CCD in FIG. 13) is changedto a drive capable of computing the focus evaluation value. Thecomputation of the focus evaluation value (“scan operation” in FIG. 13)and the display of the live image (“EVF” in FIG. 13) are concurrentlyperformed. That is, the focus lens 104 is moved to a predeterminedposition for the next image capturing before the display of the liveimage is resumed. Thus, the next AF operation can be rapidly performedand the continuous shooting interval time can be reduced.

Now referring to FIG. 12B, at step S1212, the focus evaluation value ofthe AF area set in an image capturing screen and the position of thefocus lens 104 are stored in the internal calculation memory (not shown)of the system controller 115. At step S1213, the system controller 115drives the focus lens 104 to move in a predetermined direction by apredetermined distance.

At step S1214, it is determined whether the position of the focus lens104 corresponds to the scan end position. If the position of the focuslens 104 corresponds to the scan end position (YES in step S1214), theprocess proceeds to step S1215. Otherwise (NO in step S1214), theprocess returns to step S1212, where the scan operation continues. Atstep S1215, the peak point of the focus evaluation value is computed onthe basis of the focus evaluation value and the position of the focuslens 104 stored at step S1212. Thus, the image capturing position isdetermined. At step S1216, the system controller 115 moves the focuslens 104 to the image capturing position determined at step S1215.

At step S1217, it is determined whether the focus lens 104 has reachedthe image capturing position. If the focus lens 104 has reached theimage capturing position (YES in step S1217), the process proceeds tostep S1218. Otherwise (NO in step S1217), the process returns to stepS1217, where the system controller 115 waits for the arrival of thefocus lens 104 at the image capturing position. At step S1218, thesystem controller 115 stops the computation of the focus evaluationvalue.

According to the first exemplary embodiment, as shown in FIG. 13, thesystem controller 115 can start the processes for performing the focuscontrol operation based on the contrast detection method (i.e., thedetermination of the scan range, the movement to the scan startposition, the scan operation, and the computation of the focus position)at appropriate timings concurrently with a series of the continuousshooting operations. Therefore, the focus control operation based on thecontrast detection method can be achieved within a limited continuousshooting interval time.

In addition, start of each process is controlled so that the movement ofthe focus lens 104 is prevented during readout of the main exposureimage signal. Accordingly, addition of noise to the main exposure imagesignal can be prevented, and therefore, excellent continuous shootingimages can be obtained.

As used herein, the “development process” is defined as a processstarting from the readout of the signal output from the A/D converter109 to the conversion of an image format to, for example, a JPEG format.However, the following system may be employed. That is, for example, thesignal output from the A/D converter 109 is subjected to white balanceadjustment by the white-balance (WB) processing unit 111. Thereafter,the image processing unit 110 generates an appropriate output imagesignal. These two processes are defined as the “development process”.Subsequently, when a live image can be generated, the display of thelive image is started. In this way, the file format conversion of theoutput image signal to JPEG and the display of the live image can beperformed concurrently.

Second Exemplary Embodiment

A second exemplary embodiment of the present invention is described nextwith reference to the accompanying drawings. In the second exemplaryembodiment, a focus control operation can be achieved in a system inwhich the computation of the focus evaluation value and image processingof the main exposure image signal can be performed at the same time.Additionally, in this system, the setting of the scan range of thecontinuous shooting AF can be performed earlier than that in the firstexemplary embodiment.

According to the second exemplary embodiment, the circuit configurationof an electronic camera is similar to that shown in FIG. 1. In addition,since the basic operation of the second exemplary embodiment is similarto that of the first exemplary embodiment shown in FIGS. 2 to 4,description thereof is not repeated. However, the image capturingoperation and the focus control operation in the continuous shootinginterval may be different from those of the first exemplary embodimentand are described next with reference to FIGS. 14 to 17.

FIG. 14 is a flow chart of an exemplary image capturing processaccording to the second exemplary embodiment of the present invention.At step S1300, the display of the current live image is stopped. At stepS1301, the exposure operation performed by the image pickup device 108is started. At step S1302, a continuous shooting interval AF process Afor determining a scan range is performed. This continuous shootinginterval AF process A includes a subject estimation process.

The continuous shooting interval AF process A is described in detailbelow with reference to FIG. 15. At that time, as shown in FIG. 17, amain exposure process for capturing a still image (the main exposureshown in FIG. 17) and the continuous shooting interval AF process A (thecomputation of the scan range in FIG. 17) are performed concurrently.

At step S1303, it is determined whether the main exposure has beencompleted. If the main exposure has been completed (YES in step S1303),the process proceeds to step S1304. Otherwise (NO in step S1303), theprocess returns to step S1303, where the system controller 115 waits forthe completion of the main exposure.

An image formed on the surface of the image pickup device 108 isphotoelectrically converted to an analog signal. At step S1304, theanalog signal is transferred to the A/D converter 109. The A/D converter109 performs pre-processing including reduction of output noise of theimage pickup device 108 and a non-linear process first. The A/Dconverter 109 then converts the analog signal to a digital signal.

At step S1305, it is determined whether the current set mode is acontinuous shooting mode. If the current set mode is a continuousshooting mode (YES in step S1305), the process proceeds to step S1306.Otherwise (NO in step S1305), the process proceeds to step S1308. Atstep S1306, it is determined whether the switch SW2 is continuouslydepressed. If the ON state of the switch SW2 is maintained (YES at stepS1306), the process proceeds to a continuous shooting interval B at stepS1307. The continuous shooting interval B at step S1307 is describedbelow with reference to FIGS. 16 and 17.

At step S1308, a signal output from the A/D converter 109 is subjectedto white balance adjustment by the white-balance (WB) processing unit111. The image processing unit 110 corrects this signal into anappropriate output image signal. At step S1309, the format conversionunit 112 converts the format of the output image signal to, for example,a JPEG format. The converted output image signal is temporarily storedin the DRAM 113 serving as a working memory. As used herein, the seriesof processes from steps S1308 to S1309 is referred to as a “developmentprocess”.

At step S1310, a write request is registered. The write request is usedfor requesting performance of a data write process (delayed writeprocess) in which data is written to a recording medium concurrentlywith another process. That is, the write request is used to instruct theimage recording unit 114 to store data in the DRAM 113 serving as aworking memory in a memory of the camera or on an external recordingmedium loaded in the camera, such as a memory card. Thus, the live imagecan be displayed during storing of data on the recording medium. At stepS1311, the display of the live image that has been stopped at step S1311is resumed. Then the process returns.

Thus, as can be seen from the flow chart of FIG. 14, if the continuousshooting mode is set and the switch SW2 is depressed, the continuousshooting operation is continuously performed. If one of theabove-described conditions is not satisfied, a single shooting operationis performed.

FIG. 15 is a flow chart of an exemplary continuous shooting interval AFprocess A. FIG. 15 primarily illustrates a process flow for setting ascan range for the focus control during the continuous shootinginterval. This focus control includes subject estimation.

At step S1401, it is determined whether this image capturing operationis a second image capturing operation of the continuous shootingoperation. If this image capturing operation is a second image capturingoperation (YES in step S1401), the process proceeds to step S1405.Otherwise (NO in step S1401), the process proceeds to step S1402. Atstep S1405, the current position, that is, the position of the focuslens 104 in the first continuous shooting operation is determined to bea central point of the scan range (see position (2) in FIG. 5). The samewidths of the scan range are determined so that the continuous shootinginterval time is not increased, for example, the AF operation iscompleted within the continuous shooting interval time.

At step S1402, it is determined whether this image capturing operationis a third image capturing operation of the continuous shootingoperation. If this image capturing operation is a third image capturingoperation of the continuous shooting operation (YES in step S1402), theprocess proceeds to step S1404. Otherwise (NO in step S1402), theprocess proceeds to step S1403. At step S1404, the two in-focus positioninformation items for the first image capturing operation and the secondimage capturing operation of the continuous shooting operation areavailable as in-focus position history information. Accordingly, asshown by position (3) in FIG. 5, assuming that the continuous shootinginterval time is constant, the scan middle position can be obtained bysubject estimation using a first-order approximation. Note that theparameter FpAdj(n) is a parameter for weighting the estimation result ofthe subject and the immediately previous in-focus position. The value ofthe parameter FpAdj(n) ranges from 0 to 1. At the position of the focuslens in FIG. 5, FpAdj(n)=1. As in step S1405, the widths of the scanranges are set to be the same.

At step S1403, at least three previous in-focus position informationitems are available as in-focus position history information.Accordingly, as shown by a position (4) in FIG. 5, assuming that thecontinuous shooting interval time is constant, the scan middle positioncan be obtained by subject estimation using a second-orderapproximation. As in step S1405, the widths of the scan ranges are setto be the same.

So far, the continuous shooting interval AF process A has beendescribed. As shown in FIG. 17, this process is performed concurrentlywith the main exposure process. At this point of time, since theprevious image capturing position has been determined, the subjectestimation based on the in-focus position history information can beperformed before the main exposure process is performed.

FIGS. 16A and 16B illustrate a flow chart of an exemplary continuousshooting interval AF process B. FIGS. 16A and 16B primarily illustrateoperations subsequent to the scan operation for focus control.

The development process is started at step S1501. The developmentprocess is started immediately after the readout operation of the mainexposure image signal shown in FIG. 17 has been completed. At stepS1502, it is determined whether the previous scan range settingoperation has been completed. If the previous scan range settingoperation has been completed (YES in step S1502), the process proceedsto step S1503. Otherwise (NO in step S1502), the process returns to stepS1502, where the system controller 115 waits for the completion of theprevious scan range setting operation. At step S1503, moving of thefocus lens 104 to the scan start position in the determined scan rangeis started. Accordingly, as shown in FIG. 17, the development process isconcurrently performed during the movement of the focus lens 104.

At step S1504, it is determined whether the focus lens 104 has reachedthe scan start position. If the focus lens 104 has reached the scanstart position (YES in step S1504), the process proceeds to step S1505.However, if the focus lens 104 has not reached the scan start positionyet (NO in step S1504), the process stays at step S1504, where thesystem controller 115 waits for the completion of the movement of thefocus lens 104. At step S1505, the computation of the focus evaluationvalue is started. At that time, as shown in FIG. 17, the drive of theimage pickup device 108 (the CCD in FIG. 13) is changed to the drivecapable of computing the focus evaluation value. The computation of thefocus evaluation value (“scan operation” in FIG. 17) and the developmentprocess (“development” in FIG. 17) are concurrently performed.

Now referring to FIG. 16B, at step S1506, the focus evaluation value ofthe AF area set in the image capturing screen and the position of thefocus lens 104 are stored in the internal calculation memory (not shown)of the system controller 115. At step S1507, the system controller 115drives the focus lens 104 to move in a predetermined direction by apredetermined distance. At step S1508, it is determined whether theposition of the focus lens 104 corresponds to the scan end position. Ifthe position of the focus lens 104 corresponds to the scan end position(YES in step S1508), the process proceeds to step S1509. Otherwise (NOin step S1508), the process returns to step S1506, where the scanoperation continues.

At step S1509, the peak point of the focus evaluation value is computedon the basis of the focus evaluation value and the position of the focuslens 104 stored at step S1506. Thus, the image capturing position isdetermined. At step S1510, the system controller 115 moves the focuslens 104 to the image capturing position determined at step S1509. Atstep S1511, the system controller 115 stops the computation of the focusevaluation value.

At step S1512, it is determined whether the focus lens 104 has reachedthe image capturing position. If the focus lens 104 has reached theimage capturing position (YES in step S1512), the process is completed.Otherwise (NO in step S1512), the process returns to step S1512, wherethe system controller 115 waits for the arrival of the focus lens 104 atthe image capturing position.

According to the second exemplary embodiment, as shown in FIG. 17, thesystem controller 115 can start the processes for performing the focuscontrol operation based on the contrast detection method (i.e., thedetermination of the scan range, the movement to the scan startposition, the scan operation, and the computation of the focus position)at appropriate timings concurrently with a series of the continuousshooting operations including the main exposure for capturing a stillimage. Therefore, the focus control operation based on the contrastdetection method can be achieved within a limited continuous shootinginterval time.

In addition, start of each process is controlled so that the movement ofthe focus lens 104 is prevented during readout of the main exposureimage signal. Accordingly, addition of noise to the main exposure imagesignal can be prevented, and therefore, excellent continuous shootingimages can be obtained.

Third Exemplary Embodiment

A third exemplary embodiment of the present invention is described nextwith reference to the accompanying drawings. According to the thirdexemplary embodiment, the system configuration is similar to that of thesecond exemplary embodiment. In addition, in this configuration, when anactuator operates, noise does not have a negative impact on the mainexposure image signal. For example, an actuator for driving the focuslens 104 is disposed distant from the image pickup device 108 and theA/D converter 109.

In such a configuration, since noise caused by the operation of theactuator needs not to be taken into account when the main exposure imagesignal is read out, the focus lens 104 can be moved immediately afterthe shutter is closed, as shown in FIG. 18. Accordingly, the continuousshooting interval AF process can be efficiently performed.

According to the first to third exemplary embodiments of the presentinvention, the following advantages can be provided.

(1) Moving of the focus lens 104 to the scan start position is startedafter the main exposure image is read out. Thereafter, when the focuslens 104 reaches the scan start position after an image signal forcomputation of the focus evaluation value is started to be read out, thescan operation is started. Accordingly, the development process (avariety of image processing and JPEG compression) for recording a stillimage after the main exposure is performed can be performed concurrentlywith the focus control. Consequently, the focus control operation basedon the contrast detection method can be completed within the limitedcontinuous shooting interval time. In addition, as noted above, themoving of the focus lens 104 to the scan start position is performedafter the main exposure image has been read out. Thus, noise caused bythe operation of the focus lens 104 does not have a negative impact onthe main exposure image signal, and therefore, excellent images can beobtained by continuous shooting.

(2) It is assumed that the hardware configuration is employed in whichnoise caused by the operation of the focus lens 104 does not have anegative impact on the main exposure image signal. In such a case, thefocus lens 104 is moved to the scan start position after the shutterblocks light for the main exposure. After readout of an image signal forcomputation of the focus evaluation value is started and the focus lens104 reaches the scan start position, the scan operation is started.Accordingly, after the main exposure is performed, the developmentprocess (a variety of image processing and JPEG compression) forrecording a still image can be performed concurrently with the focuscontrol. Consequently, the focus control operation based on the contrastdetection method can be completed within the limited continuous shootinginterval time.

(3) The focus lens 104 is moved to the scan start position after thereadout of the main exposure image has been completed. Thereafter, whenthe focus lens 104 reaches the scan start position after the developmentprocess has been completed, the scan operation is started. Accordingly,the start timing of the scan operation can be controlled so as to avoida variety of constrained cases. Examples of the constrained case includea) a case where the following concurrent operations are difficult: ahigh-load process for the system, such as the development process (avariety of image processing and JPEG compression) for recording a stillimage after the main exposure is performed, and the focus evaluationvalue acquirement operation by the contrast detection method thatrequires the signal processing; and b) a case where the followingconcurrent operations are difficult due to the hardware resourceconflict: the development process and the focus evaluation valueacquirement operation that require the same resource. Consequently, bytaking into account the system load and the hardware resource conflict,the focus control operation based on the contrast detection method canbe completed within the limited continuous shooting interval time. Thus,noise caused by the operation of the focus lens 104 does not have anegative impact on the main exposure image signal, and therefore,excellent images can be obtained by continuous shooting.

(4) It is assumed that the hardware configuration is employed in whichnoise caused by the operation of the focus lens 104 does not have anegative impact on the main exposure image signal. In such a case, thefocus lens 104 is moved to the scan start position after the shutterblocks light for the main exposure. After readout of an image signal forcomputation of the focus evaluation value is started and the focus lens104 reaches the scan start position, the scan operation is started.Accordingly, the start timing of the scan operation can be controlled soas to avoid a variety of constrained cases. Examples of the constrainedcase include a) a case where the following concurrent operations aredifficult: a high-load process for the system, such as the developmentprocess (a variety of image processing and JPEG compression) forrecording a still image after the main exposure is performed, and thefocus evaluation value acquirement operation by the contrast detectionmethod that requires the signal processing; and b) a case where thefollowing concurrent operations are difficult due to the hardwareresource conflict: the development process and the focus evaluationvalue acquirement operation that require the same resource.Consequently, by taking into account the system load and the hardwareresource conflict, the focus control operation based on the contrastdetection method can be completed within the limited continuous shootinginterval time.

(5) When the scan range setting process of computing the central pointand the width of the scan range on the basis of a history of thepositions of the focus lens 104 in the previous image capturingoperations is performed, a variety of approximation calculations arerequired to estimate the movement of a subject. In addition, a certaintime may be required until the scan range setting process is completed.However, according to the present invention, the scan range computationprocess can be completed between the time the image capturing positionfor the previous image is determined and the time the moving of thefocus lens to the scan start position is started for the next scanoperation. Accordingly, for example, the scan range setting process forthe next image to be captured can be performed in advance while thefocus lens 104 moves to the image capturing position or the mainexposure is performed. Consequently, the focus control operation basedon the contrast detection method can be efficiently performed within thelimited continuous shooting interval time.

(6) During the computation of the focus evaluation value, a live imagecan be generated and displayed on the basis of image signalsperiodically output from the image pickup device 108. That is, in thefocus control operation based on the contrast detection method, asubject image is captured by the image pickup device 108 at apredetermined interval and the focus evaluation value is computed on thebasis of the signals of the subject image. At that time, the imagesignal output from the image pickup device 108 is used not only for thecomputation of the focus evaluation value, but also for the display ofthe live image. Consequently, the live image can be displayed in thecontinuous shooting interval time, and therefore, a photographer caneasily recognize the change in the subject during the continuousshooting interval time.

As can be seen from the foregoing description, according to the first tothird exemplary embodiments of the present invention, the electroniccamera can start the processes for performing the focus controloperation based on the contrast detection method at appropriate timingsconcurrently with a series of the continuous shooting operations.Consequently, the focus control operation based on the contrastdetection method can be efficiently performed within the limitedcontinuous shooting interval time. In addition, the electronic cameracontrols start of each process so that the movement of the focus lens104 is prevented during the main exposure and readout of the mainexposure image signal. Thus, blur of a recorded image and addition ofnoise to the main exposure image signal can be prevented, and therefore,excellent images can be obtained by continuous shooting.

That is, the focus control during the continuous shooting interval canbe achieved and excellent images can be obtained by continuous shooting.Accordingly, unlike existing electronic cameras, a cost-effectiveelectronic camera having a compact size and that does not waste thecapacity of a recording medium can be provided.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures and functions.

1. An image pickup apparatus having a continuous shooting mode in whicha plurality of images are captured for recording in response to an imagecapture instruction, wherein respective development process for eachimage is performed before capturing a subsequent image for recording inthe continuous shooting mode, the image pickup apparatus comprising: afocus control unit configured to detect a focal point of a focus lens bymoving the focus lens in a light axis direction thereof across apredetermined range to perform a scanning and control movement of thefocus lens so that the focus lens is focused at the focal point; and acontrol unit configured to control movement of the focus lens and tocontrol the capturing of an image, wherein, after the control unitcontrols the movement of the focus lens using the focus control unit andcaptures an image for recording in the continuous shooting mode, thecontrol unit moves the focus lens to a predetermined position and thenmoves the focus lens across the predetermined range from thepredetermined position to perform the scanning using the focus controlunit during the development process of the captured image beforecapturing the subsequent image for recording.
 2. The image pickupapparatus according to claim 1, wherein the control of the movement ofthe focus lens for the subsequent image capturing operation forrecording by the focus control unit is performed during a readoutprocess of the captured image from an image pickup device.
 3. The imagepickup apparatus according to claim 1, wherein the control of themovement of the focus lens for the subsequent image capturing operationfor recording by the focus control unit is started during thedevelopment process of the captured image.
 4. (canceled)
 5. An imagepickup apparatus having a continuous shooting mode in which a pluralityof images are captured for recording in response to an image captureinstruction, the image pickup apparatus comprising: a focus control unitconfigured to detect a focal point of a focus lens by moving the focuslens in a light axis direction thereof across a predetermined range toperform a scanning and control movement of the focus lens so that thefocus lens is focused at the focal point; a memory configured to storecaptured images; an instructing unit configured to instruct a displayunit to display the images before recording the images in the memory;and a control unit configured to control movement of the focus lens andto control the capturing of an image, wherein, after the control unitperforms the scanning using the focus control unit and captures an imagefor recording in the continuous shooting mode, the control unit starts asubsequent scanning before the display unit displays captured image. 6.The image pickup apparatus according to claim 5, wherein, in thecontinuous shooting mode, a position from which detection of the focalpoint is performed by the focus control unit is determined based on theposition of the focal point detected by the previous scanning. 7-10.(canceled)